Anubis

Anubis flys around and shoots purple circles from his Sceptre that kill you in one hit. The purple circles traverse through walls, but move slowly. He can only be found in 4-1.

The easiest way to kill Anubis is by using Paste and bombs. Bombs travel through the purple circles without their trajectory being altered. Paste causes the bombs to stick to Anubis. Two bombs kill him.